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On Mon, 10 Aug 2009, Timo Sirainen wrote:
4. Implement a multi-master filesystem backend for index files. The idea
would be that all servers accessing the same mailbox must be talking to
each others via network and every time something is changed, push the
change to other servers. This is actually very similar to my previous
multi-master plan. One of the servers accessing the mailbox would still
act as a master and handle conflict resolution and writing indexes to
disk more or less often.
What I don't understand here is:
_One_ server is the master, which owns the indexes locally?
Oh, 5. means that this particular server is initiating the write, right?
You spoke about thousends of servers, if one of them opens a mailbox, it
needs to query all (thousends - 1) servers, which of them is probably the
master of this mailbox. I suppose you need a "home location" server, which
other servers connect to, in order to get server currently locking (aka
acting as master for) this mailbox.
GSM has some home location register pointing to the base station currently
managing the user info, because the GSM device is in its reach.
There is also another point I'm wondering about:
index files are "really more like memory dumps", you've wrote. so if you
cluster thousends of servers together you'll most probably have different
server architectures, say 32bit vs. 64bit, CISC vs. RISC, big vs. little
endian, ASCII vs. EBCDIC :). To share these memory dumps without another
abstraction layer wouldn't work.
5. Implement filesystem backend for dbox and permanent index storage
using some scalable distributed database, such as maybe Cassandra. This
Although I like the "eventually consistent" part, I wonder about the
Java-based stuff of Cassandra.
is the part I've thought the least about, but it's also the part I hope
to (mostly) outsource to someone else. I'm not going to write a
distributed database from scratch..
I wonder if the index-backend in 4. and 5. shouldn't be the same.
===
How many work is it to handle the data in the index files?
What if any server forwards changes to the master and recieves changes
from the master to sync its local read-only cache? So you needn't handle
conflicts (except when network was down) and writes are consistent
originated from this single master server. The actual mail data is
accessed via another API.
When the current master does no longer need to access the mailbox, it
could hand over the "master" stick to another server currently accessing
the mailbox.
Bye,
- --
Steffen Kaiser
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